Fedora 17 boot loader should be installed on MBR or logical partion on MBA2012?

Well,now I've a DUAL-boot-OS(win7+lion10.7.4) mac book air 2012 with rEFIt installed . I'm wondering about where to install the fedora17 boot loader, on MBR or fedora partion? When I select to install on /dev/sda6(mount point /), system exception occured, no further operation can be performed.
If I install the Fedora 17 boot loader on MBR of MAC local drive, will it destroy the booting of MAC OS and windows7 system? I do NOT wanna lose the previous data.